New Evidence Supports Old Theory of Cancer Spread

"Cancer cells exhibit a remarkable number of traits normally attributed to white blood cells known as macrophages, including the ability to migrate to lymph nodes and distant organs and to form a new blood supply. Our data indicate that they do this by hybridising with macrophages," said lead author John Pawelek, research affiliate in the Department of Dermatology at Yale School of Medicine and a member of Yale Cancer Center.

Pawelek said the idea of white blood cells hybridising with tumour cells is not new. In the early 1900's the German pathologist Otto Aichel proposed that metastasis is caused by cancer cells fusing with macrophages. "There is now evidence to support all aspects of his proposition," said Pawelek. "Macrophages are among the most motile cells we have. By co-opting the macrophage's ability to move, the hybrid is very different from the original cancer cell. It is able to migrate away from the primary site of tumour formation and take up residence in other areas of the body while it continues to divide."

Pawelek concludes that there is now sufficient evidence for Aichel's proposal to be taken seriously by the research community. Pawelek's group began testing the theory in 1993, when they created hybrids in the lab by fusing mouse melanoma cells with mouse macrophages. “Their behaviour was astonishing," said Pawelek. "In culture dishes, fused cells were extraordinarily motile compared to unfused melanoma cells. They spread rapidly when implanted in mice."

"Aichel implored future scientists to study cancer cells 'from all angles' for evidence of hybridisation," Pawelek added. "It is remarkable that a century later we are doing just that."